The Hailey Fire Department and Wood River Fire and Rescue responded Saturday evening to a report of smoke coming from the basement of Rocky Mountain Hardware's new building in Hailey, which is still under construction.
Firefighters arrived at the scene, located on the Main Street end of Airport Way, just before 6 p.m.
Mike Chapman, Hailey's fire chief, said that thermal imaging was used to locate the point of origin of the fire.
"It was difficult as there were no visible flames and the basement was filled with a thick, acrid smoke," Chapman said Monday.
The smoldering material was quickly put out using portable extinguishers.
The cause of the fire was determined to be the result of a piece of welding slag that had fallen from an upper level into the basement, igniting low-density particle board and spools of rubber-coated wire.
Six firefighters from Hailey were at the scene, along with a crew of five from Wood River. The Bellevue Fire Department was also on stand-by in case the fire escalated.